A commonly found safety-related component in government facilities, commercial nuclear power plants, and navy power plants is a motor operated or actuated valve. Such valves perform a wide range of safety related functions, from for example, containment isolation to controlling high-pressure coolant injection, as these are particularly well understood in the nuclear power area. Unfortunately, conventional valve actuator designs may often present operation and/or control problems.
In nuclear power plant situations, U.S. and international regulators have responded to such operational and control problems by requiring frequent and rigorous testing and adjustments for all of the motor-operated valves in nuclear power plants. Such testing is both time consuming and expensive.
Some of the problems of conventional motor-operated valves may be inherent in the respective designs thereof. For example, many conventional valves are highly torque dependent. The motors associated therewith output a high torque rotational motion. However, many of the actual valves are of a type having a rising valve stem which requires a substantially linear thrust load. For relatively small valves the currently available directly acting or geared actuators are often satisfactory. But, when high seating and unseating forces are required, as in the case of large diaphragm, gate and/or globe valves, the currently available actuators are often exceedingly complex with highly-specialized motors being required to give the high torques necessary to provide the desired valve movement forces to open and/or close the valve.